Shaped Charges, Devices, General:
A shaped charge in the broadest context is any piece of high explosive (“HE”) material shaped to perform a specific task lined or unlined. There are basically two types of shaped charges, Axisymmetric and Linear or planer symmetric. By far the most common type of shaped charge is the axisymmetric conical lined shaped charge. These charges, commonly used in anti-armor and oil well perforating, are essentially a hollow cylinder containing a hollow cone type metal liner having explosive material filling the remaining space in the cylinder aft of the cone. Liners are usually made from copper, although it could be made of many other materials, having an explosive billet to which the outside of the liner is exactly mated.
When the explosive material contained in a shaped charge is detonated at the center of the aft end of the explosive, above the apex or pole of the liner, a detonation wave spreads spherically into the explosive material, in the process collapsing the liner into a rod like stretching projectile commonly called a jet. There is another less known form of shaped charge called a linear shaped charge that collapses its liner into a sheet like jet, it is useful in many applications and can be safely fabricated and used.
A Linear shaped charge, sometimes referred to as a line charge, is essentially a V shaped straight hollow thin walled trough liner backed on the outside of the V by an appropriately shaped explosive mass. When intentionally detonated above the apex of the liner, this linear shaped charge produces sheet or ribbon like jetting.
Present day conventional Linear shaped charges (LSC) consist of a thin, flat-walled, long hollow trough-like liner, backed on the outside by a correctly shaped amount of explosive, contained in a body and having an initiation system. When the explosive is intentionally detonated above the apex of the liner the explosive pressure drives the two sides of the trough together producing a sheet or ribbon like jet that cuts a slot approximately the length of the linear shaped charge. These special purpose devices are generally short in length and are initiated at a single point or maybe multiple points along the crown of the HE billet. This type of initiation does not produce a well-defined or controllable jet, the leading edge is ragged and penetration depth inconsistent along its length. The standard smooth wall linear shaped charge gives only a two-dimensional collapse (a result of no liner wall axial curvature) of the liner material and typically produces an explosively formed projectile rather than a jet and slug.
Conventional LSC consist of a rectangular block of explosive with an angular valley in one of its long sides lined with a thin metal liner. Typically, conventional LSC produce sheet projectile velocities from about 1.5 to 2.2 km/s, with little to no jet material velocity gradient and consequently shorter jet and less penetration. The sheet jets have a ragged leading edge because of the non-simultaneous linear initiation system. Conventional LSC do not penetrate hydro dynamically, the same way axisymmetric (i.e. conical) shaped charges do, it is the shaped mass and velocity of the sheet jet that shears the material with brute force leaving large burrs or flaring of the casing in an oil well application.
The jetting occurring in a conventional LSC is not Munroe jetting as the collapse is only two dimensional (does not have axisymmetric convergence) and does not reach the required temperature for plastic flow to take place. As a further recognition of the inefficiency of a conventional LSC the detonation wave does not reach the full length of the liner apex simultaneously, this causes an undesirable dispersion of the resulting spray of liner material and no real continuity to the spray.
Conventional planer symmetric “V” shaped linear liners used in LSC have no curvature or radial convergence and produce low velocity jets. Conventional LSC have large explosive to liner mass ratios and form low velocity (about 2.0 km/s) thin blade or ribbon jet that produce shallow target cuts (mostly non-plastic erosion much like water jet cutting). Conventional LSC are non-precision, low efficiency, cutting charges, without axisymmetric radial convergence the explosive mass must be increased greatly to create the very high pressures needed to produce a very thin ribbon jet from the linear liner; because of the high HE mass most of the penetration from a conventional LSC is made from the hollow cavity effect of the explosive with very little penetration from the liner. Because of their large HE to liner mass ratio conventional LSC can't make precision deep target cuts or penetrations and typically produce a wide cratering effect from the collateral damage of the large amount of explosive.
Conventional LSC have not been researched, developed, refined or used to the extent that axisymmetric shaped charges have. There are many undesirable aspects of existing conventional LSC such as a two-dimensional collapse, the lack of a simultaneous initiation system, and poor penetration performance. The poor and inconsistent performance is primarily because of the lack of a simultaneous initiation along the full length of the explosive billet and the two-dimensional collapse from a smooth walled liner.
Accordingly, there is a need in the art for a better performing LSC. Therefore, this inventor has conducted experiments and invented a novel improvement to LSC and their jetting performance.